It has furthermore been found that the use of specific cationic surfactants (b) also makes it possible to raise the color intensity of cationic azo dyes of formula (I). Another subject matter of the present disclosure is therefore the use of specific cationic surfactants (b) to improve the color take-up performance of cationic azo dyes of formula (I) onto keratinous fibers.
As a general rule, either direct dyes or oxidation dyes may be used for dyeing keratinous fibers. Although intense colors with good fastness properties can be obtained with oxidation dyes, the development of the color generally takes place under the influence of oxidizing agents such as H2O2, for example, which in some cases may result in damage to the fiber. Furthermore, some oxidation dye precursors or certain mixtures of oxidation dye precursors may have a sensitizing effect on people with sensitive skin. Direct dyes are applied under gentler conditions. The disadvantage of these dyes, however, lies in the fact that the colors often have inadequate fastness properties.
A person skilled in the art uses direct dyes of different dye classes depending on the desired color result. The direct dyes known from the prior art include, for example, the classes of nitro dyes, anthraquinone dyes, azo dyes, triarylmethane dyes, or methine dyes. All of these dye classes should meet a specific requirement profile for use in the field of cosmetics. Thus, direct dyes should deliver an intense dyeing result and possess the best possible fastness properties. The color result obtained with direct dyes should be affected as little as possible by environmental influences, i.e., the dyes should have, for example, favorable wash fastness, light fastness, and friction fastness. The color result should also be altered as little as possible by chemical influences to which the keratinous fibers may be exposed after the dyeing process (e.g., permanent waves).
In order to bleach simultaneously with the dyeing, the direct dyes should also be as compatible as possible with the oxidizing agents (e.g., hydrogen peroxide and/or persulfates) commonly used in blonding processes.
For intense bleaching of dark hairs, hydrogen peroxide is not used alone, but rather a combination of hydrogen peroxide and persulfates (e.g., ammonium persulfate, potassium persulfate, and/or sodium persulfate). If, then, dark hair is to be bleached intensely in one step and simultaneously dyed in a bright shade, it is advantageous to use a mixture of hydrogen peroxide, persulfates, and a direct dye. Although many intensive-dyeing direct dyes would be known to a person skilled in the art in order to dye hair, a person skilled in the art only knows a very limited selection of dyes that exceed the strong oxidative conditions, such as represented by a mixture of the above-mentioned oxidizing agents, without decomposition. In addition, the oxidation-stable dyes that are known in the prior art have serious drawbacks with respect to the other fastness properties thereof.
There has thus been a need for dies that have high stability against strong oxidizing agents, in order to simultaneously dye and intensely bleach hair. These dyes should also not lose the positive fastness and dyeing properties thereof, even under these extreme usage conditions.
It has been shown that bright and intense coloration can be achieved, in particular, with cationic direct dyes. Cationic dyes are often distinguished by particularly elevated affinity for keratin fibers, a characteristic which may be attributed to the interactions of the positive charges of the dyes with negatively charged structural components of the keratinous fibers. Accordingly, it is often possible to achieve particularly intense colorings with cationic dyes.
Examples of well-known monomeric cationic azo dyes known from the prior art include the representatives Basic Orange 31 (alternative name: 2-[(4-Aminophenyl)azo]-1,3-dimethyl-1H-imidazolium chloride, CAS-Nr. 97404-02-9) and Basic Red 51 (alternative name: 2-[((4-Dimethylamino)phenyl)azo]-1,3-dimethyl-1H-imidazolium chloride, CAS-Nr. 77061-58-6).
Both dyes dye keratinous fibers with excellent color intensity in orange to red shades. There is still also a need for direct blue dyes that are optimally compatible with both of these dyes.